Heated glass panels are known in the art and are commonly used to reduce or prevent the formation of condensation or fog on the glass panels. For example, heated glass panels are commonly used in refrigerated merchandiser units of the type used in grocery stores to store and display refrigerated and frozen foods. Heated glass panels may also be used in other applications, such as bathroom mirrors and skylights, wherein it is desirable to reduce or eliminate the formation of condensation on the glass panels. Heated glass panels, typically in the form of windshields, also may be used in automobiles and aircraft in order to provide windshields that may be readily cleared of accumulated condensation.
While many different configurations for heated glass panels have been developed and are being used, a commonly used configuration involves at least one glass panel or “lite” having a transparent, electro-conductive surface coating or film formed thereon. Commonly used electro-conductive films include tin oxide, indium oxide, and zinc oxide, although other compositions are known and may be used as well. The electro-conductive film is not a perfect conductor, and typically possesses an electrical resistance in a range of tens to hundreds of ohms “per square.” Thus, an electric current flowing in the electro-conductive film will result in the formation of heat in proportion to the resistance of the film and the square of the current flowing in the film.
While commonly used configurations for such heated glass panels work well were the amount of heat produced is modest, such as, for example, in applications wherein the formation of condensation is to be avoided, considerable problems arise in applications wherein greater amounts of heat are to be produced. For example, it has been recognized that heated glass panels could be used to advantage in residential and commercial applications to meet at least some, if not all, of the heating requirements of the buildings in which the heated glass panels are used. However, it has proven difficult to provide an electrical connection between the power source and the electro-conductive film that is capable of reliably providing the higher currents required to produce significant amounts of heat.
In a typical configuration, thin conductors or “bus bars” positioned along opposite edges of the glass panel are used to electrically connect the electro-conductive film to a source of electrical power. The bus bars typically comprise thin strips of metal foil that are placed in contact with the electro-conductive film. While bus bars formed from such thin metal foils have been used with success in low power applications (e.g., panel de-fogging), they are not capable of handling the higher currents involved in situations where the heated glass panels are to provide a significant amount of heat. While thicker conductors could be used, it has proven difficult to provide uniform contact between the thicker conductors and the electro-conductive film. For example, small gaps or spaces between the conductors and the film may result in uneven heating of the film. In addition, such small gaps or spaces may result in the formation of arcs or sparks between the conductors and the film, which can be deleterious to the film, the conductors, or both.
Partly in an effort to address some of these problems, systems have been developed in which the conductors or bus bars are deposited on the electro-conductive film by flame spraying. While such systems have been used to produce conductors capable of handling the higher currents required for higher power dissipation, they tend to be difficult to implement, requiring expensive equipment and highly trained personnel. In addition, thickness variations in the sprayed-on metal coating may create hot spots and non-uniformities in the electrical current in the film, both of which can adversely affect the performance of the system.